The present invention relates to a liquid-crystalline polymeric composition. More particularly, the invention relates to a liquid-crystalline polymeric composition freed from the problem of phase separation by the combined use of a low molecular liquid-crystalline compound and a non-liquid-crystalline polymeric compound each having a hydrogen bond-forming group.
Various kinds of low-molecular liquid-crystalline compounds are known in the prior art but none of known low-molecular liquid-crystalline compounds is satisfactory, as an inherent property of low-molecular compounds in general, in respect of the shape retainability, i.e. a property of a material capable of being shaped into any desired form.
Liquid-crystalline materials having improved shape retainability have been proposed including a composition which is a mere blend of a polymeric compound and a low-molecular liquid-crystalline compound and a polymeric compound obtained by covalent bonding molecules of a low-molecular liquid-crystalline compound to the main chain or to the side chains of the polymeric molecule.
The above mentioned composition of polymeric compound and low-molecular liquid-crystalline compounds, however, cannot be a uniform blend microscopically but has a structure of a matrix phase and a discretely dispersed phase therein because low-molecular liquid-crystalline compounds usually have one or more methyl groups at the molecular ends. Such a microscopically inhomogeneous condition of the composition is responsible for various drawbacks when the composition is used as a liquid crystal. Due to the non-uniform distribution of the low-molecular liquid-crystalline compound in the matrix of the polymeric compound, for example, the response of the polymeric composition as a liquid crystal may sometimes be non-uniform and a liquid-crystal display elements by using such a polymeric composition may exhibit decreased sharpness.
It is also not an easy and versatile way to prepare a polymeric liquid-crystalline compound having a low-molecular liquid-crystalline compound bonded to the polymeric structure by covalent bonding because the possibility of a covalent bonding formed therebetween depends on the reactivity of the respective functional groups and the reaction conditions to match the reactivity.
One of the inventors with another has previously proposed a liquid-crystalline polymeric composition having excellent shape retainability and suitable as a liquid crystal material in optoelectronic devices and the like, which is a blend of a low-molecular liquid-crystalline compound with a non-liquid-crystalline polymeric compound capable of forming a hydrogen bond therebetween (see PCT/JP87/00521). This polymeric liquid-crystalline composition, however, is still not quite satisfactory when a high-speed response is required for the liquid-crystalline composition.
While liquid-crystalline materials in general can be used in liquid-crystal display elements, the type of display in most of modern liquid-crystal display elements is the so-called TN (twisted nematic) type using liquid-crystalline materials belonging to the nematic phase. Though advantageous in respect of eye fatigue and electric power consumption as a light-receiving type, liquid-crystal displays of the TN type have problems of relatively slow response and invisibility of the display when viewed at a certain angle. Various attempts have been made to improve liquid-crystalline materials in order to comply with the demand in recent years for display units having high-speed responsivity. The shortest response time obtained in a liquid-crystal display unit, however, is still far from satisfactory when comparison is made with other light-emitting displays such as electroluminescence displays, plasma displays and the like. There would be no other way than to develop a novel type of liquid-crystal display with which the TN-type liquid-crystal display can be replaced in order to obtain high-speed responsivity comparable with that of light-emitting type displays by retaining the advantages of the light-receiving type liquid-crystal displays of low power consumption. N. A. Clarke, et al. have proposed a type of display by utilizing the phenomenon of optoswitching of a ferroelectric liquid-crysatlline material as one of the attempts along this line [see Appl. Phys. Lett., volume 36, page 899 (1980)]. Ferroelectric liquid-crystalline materials have been first disclosed by R. B. Meyer, et al. in J. de Phys., volume 36, page L-69 (1975) and include those belonging to the chiral smectic C phase, chiral smectic I phase, chiral smectic F phase, chiral smectic G phase and chiral smectic H phase, referred to hereinbelow as the S.sub.C * phase, S.sub.I * phase, S.sub.F * phase, S.sub.G * phase and S.sub.H * phase, respectively, in the liquid-crystalline structure.
A liquid-crystal display utilizing the optoswitching effect of the S.sub.C * phase is advantageous over the TN-type liquid-crystal displays in three respects. The first advantage is the extremely high responsivity with a response time which is 1/100 or below of the response time in conventional TN-type liquid-crystal display units. The second advantage is the memory effect which enables time-sharing driving of the display as combined with the above mentioned high-speed responsivity. The third advantage is that the display can be imparted with a gradient between brightness and darkness without difficulty. In the TN-type liquid-crystal displays, such a gradient of density must be obtained by controlling the voltage of impression so that difficult problems are unavoidably encountered in connection with the temperature dependency of the threshold voltage and the voltage dependency of the speed of response. In contrast thereto, the desired gradient of density can be easily obtained in the liquid-crystal display unit utilizing the optoswitching effect of the S.sub.C * phase by controlling the reversal time of the polarity so that the display units of this type are particularly suitable for graphic displays and the like.